1. Field of the Invention
The present invention relates to a color sensor system for the recognition of objects and surfaces that are at least partially colored.
2. Description of the Prior Art
Color is a very important factor in maintaining the overall quality of food products and manufactured goods. Because the color of a product is often equated to quality, it is highly desirable to be able to control the product processing based on a color measurement to maintain consistency and adhere to specified product standards. By incorporating a color sensing system on the production line, more products can be monitored than with recognized off-line measurement techniques. Currently available color sensor technology has a number of deficiencies, limiting application thereof in many areas.
In one prior art color recognition system, the object to be analyzed for color content is illuminated with a white light, for example, the light from a halogen lamp can be used. The reflected light from the object is analyzed by means of lenses and standard color filters to split the reflected light into the primary colors, red, green and blue. The intensity of the individual color components is then converted into electrical signals by photo sensors, one for each color, which are connected to receiving amplifiers. One example of such a photo sensor is a light sensitive photodiode. In these systems, the transmitting light generator and the light receiver and amplifiers are located in close proximity to the object or the surface to be color analyzed which is often a problem in many food processing or manufacturing operations. Also, halogen light sources have a relatively short life span and shutdown of the production line is required for replacement.
For longer life, LEDs can be used as a light source. In another prior art color recognition system, the object to be analyzed for color content is illuminated with the light emitted by a plurality of light emitting diodes (LEDs) where each diode emits light energy in a narrow-band range of wavelengths. Commonly, LEDs emitting red, green and blue colored light are used for illumination. The reflected light from the object is then analyzed for color content.
Separate LEDs are used for orange (or red), green and blue light all of which emit different amounts of light energy. Again, the color measurement of the object is affected by the imbalance of the LED light energy that is used to illuminate the object whose color is to be analyzed and the imbalance of the spectral response of the receiver. LEDs and sensors which are used on-line frequently have their sensing heads and light source and processing logic separated by bundles of fiber optic cables wherein the termination of the transmitting and receiving end of the fiber optic cable is positioned closely spaced from the object while the other components are physically remote to protect them from the manufacturing process or to overcome space limitations.
A modulated color sensor system is known which has a plurality of electronic light transmitters (e.g. LEDs) emitting light of various wavelengths which, in succession, briefly illuminate an object whose color is to be determined with light pulses. The light reflected from the object is directed to a photo sensor, which converts the light signals into electrical signals for eventual evaluation for color content. By using a threshold light indicator (checking each color in succession) no provision is made for a quantitative evaluation of the intensity of the individual color components, such as is necessary for a determination of mixed colors and the result is an inaccurate color spectrum.
U.S. Pat. No. 4,917,500 the disclosure of which is incorporated herein by reference, describes a color sensor system that accounts for the relative intensity of the individual color components. The system employs at least three light emitting diodes (LEDs) emitting light pulses in a predetermined narrow-band range of wavelengths and an identical transmitting optical fiber bundle associated with each LED. A light receiving optical fiber bundle is packaged with the transmitting optical fiber bundles so that the reflected light from the colored surface of the object is transmitted through the optical fiber bundle to a light receiver having a photo semiconductor. The optical fiber bundles can be assembled together in one sensor head. The problem with this system is that for a given signal to noise ratio, the size of the sensor head is not minimized.